1. Field of the Invention
This invention relates to a method for controlling the breathing gas flow of a ventilator for assisted or controlled ventilation of a patient as a function of the tracheobronchial airway pressure of the patient, having a ventilator tube, such as a tracheal tube or tracheostomy tube, that can be introduced into the trachea or the patient and subjected to the breathing gas, that has an inflatable cuff and at least one lumen that is continuous from the distal end of the tube to the proximal end of the tube. This invention also relates to an apparatus for detecting the airway pressure, in which the tracheobronchial airway pressure is determined by continuous or intermittent detection and evaluation of the intra-cuff pressure prevailing in the cuff of the tube inserted into the trachea, and the breathing gas flow of the ventilator is controlled as a function of the intra-cuff pressure detected.
This invention also relates to a system for assisted or controlled ventilation of a patient, having a ventilator with a breathing gas source and a ventilator tube, which has an inflatable cuff with a supply line for compressed air, such as a tracheal tube or tracheostomy tube, which can be connected to the breathing gas source, an apparatus for detecting the airway pressure, and a control device which as a function of patient values, such as the airway pressure, controls the ventilator, or the supply quantity and composition of the breathing gas to the tube.
This invention also relates to the use of a ventilator tube, such as a tracheal tube or tracheostomy tube, or a gastric probe in a system for assisted or controlled ventilation of a patient with a ventilator.
2. Description of Related Art
A ventilator for assisted or controlled ventilation, with a ventilator tube and a breathing gas source that can be made to communicate with the ventilator tube and is controllable with patient values, is known from European Patent Disclosure EP 0 022 144 A1. With the aid of the control device of the ventilator, respiratory parameters such as tidal volume, respiratory rate, respiratory minute volume, flow pattern over time, end-inspiratory pause, amplitude of the breathing gas flow, pressure at the end of inspiration, peak pressure, PEEP pressure, idle volume in the ventilator, and ventilator compliance, can be adjusted.
In all the known ventilators and ventilation methods known, the so-called ventilation pressure, that is, the airway pressure (Presp) prevailing in the airways, is output as a parameter or is used as a parameter in the control algorithms of the ventilator. In clinical practice, Presp is typically ascertained inside the ventilator, or in the tubing leading to the patient. The airway pressure measured in the ventilator, because of the flow-dependent flow resistance inside the equipment, vent hoses, and ventilator tube, however, often differs considerably from the so-called central or tracheobronchial airway pressure (Ptrach) prevailing in the trachea of the patient. It is therefore difficult to draw a conclusion about the central airway pressure actually achieved in the trachea from the ventilation pressure measured inside the ventilator.
European Patent Disclosure EP 0 459 284 B1 teaches measuring the central airway pressure via a pressure measuring hose additionally placed in the trachea or in the tracheal tube, or via a fluid-filled pressure measuring conduit machined into the wall of the tracheal tube. The tracheobronchial airway pressure thus is intended to provide improved control of ventilators with supporting spontaneous breathing modes. A disadvantage in this measuring method for detecting the tracheobronchial airway pressure using pressure hoses in accordance with European Patent Disclosure EP 0 459 284 B1 is that the thin pressure measuring hoses, placed in the trachea in the tracheal tube, rapidly plug up with secretions on their end oriented toward the bronchial tube, and thus the central airway pressure can no longer be measured reliably. The pressure measuring hoses must be rinsed out from time to time. An apparatus according to European Patent Disclosure EP 0 459 284 B1 for measuring the tracheobronchial airway pressure using pressure measuring hoses or pressure measuring conduits that are filled with fluid has not yet gained acceptance, mainly because of the high cost of equipment and the expected vulnerability to malfunction, or the resultant measurement imprecision.
German Patent Disclosure DE-A 32 04 110 discloses a tracheal tube that includes a ventilation hose and a pressure measuring cannula for measuring the airway pressure. The pressure measuring hose ends inside the ventilator tube, at a distance from the distal end of the ventilator tube. This apparatus is again used to detect the airway pressure for regulating ventilation control with a ventilator. This apparatus for detecting the central airway pressure again has the disadvantage that the pressure measuring cannula, which is open on its end toward the bronchial tube, easily becomes plugged with secretions, making reliable, artifact-free measurement and regulation of the ventilator impossible.
PCT International Application WO 94/22518 teaches a ventilator tube which is used to control a ventilator. For continuous measurement of the central tracheobronchial airway pressure in assisted or controlled ventilation, the ventilator tube has a pressure sensor, located near the distal end of the ventilator tube. The pressure sensor is connected to an electronic signal processor, and the signal obtained is used to control various functions in the ventilator. Such a method is technologically complex and once again, because of deposits of secretion on the sensor, is adequately invulnerable to malfunction.